This invention relates to proofing machines and particularly to the exposure mechanism and to the proof retaining means of the machine.
In printing trade publications for example, after the production of the film negatives and before the final film or printing plates are made, proofs are required to verify the position of the material on the page and its content. Proofs are normally produced by exposing a light sensitive material through the negatives--which may be done in sections while masking the balance of the light sensitive material to build up a page. One material for producing proofs of this nature is DYLUX, a product of E.I. duPont de Nemours and Co. which, when exposed to ultraviolet light, provides a blue-tinted proof that can be readily reviewed.
Proofing machines usually include means for locating the negatives relative to the film and means such as a vacuum for holding the film and the negative firmly in contact during exposure. In machines such as the one disclosed in U.S. Pat. No.3,176,601, pages are exposed one at a time and the machines are therefore slow. To provide for multiple exposures would be complicated by the difficult alignment and holding problems with the negatives as represented by the positioning pins 97 and vacuum channels 92 through 96 of U.S. Pat. No. 3,176,601, and would be particularly difficult in view of the need for versatility in accommodating negatives and films of different sizes. U.S. Pat. No. 4,529,303 also shows a vacuum frame for holding a photosensitive plate while it's being exposed in which there is also provided positioning pins for the work.
Using a light carriage advanced over the work for continuous exposure such as disclosed for example in U.S. Pat. No. 3,644,039 requires that the light carriage be advanced at a precise rate to obtain the proper exposure. This requires a drive mechanism that not only represents an expense but also requires time as the carriage moves at the preselected rate over the film.